DRAFT VERSION 1 Whangarei District Natural Hazard Constraints Report Prepared by: David Coleman 10 July 2009 Table of Contents 1.0 Introduction....................................................................................................5 1.1 Natural Hazards: A Briefing....................................................................................5 1.2 Natural Hazard Risk ..............................................................................................6 2.0 Biophysical Profile and Hazardscape of Whangarei..........................................9 3.0 Individual Hazard Types................................................................................13 3.1 Flood Hazards .................................................................................................... 13 3.2 Extreme Weather Events ..................................................................................... 19 3.3 Coastal Hazards.................................................................................................. 21 3.4 Extreme Weather Events: Droughts....................................................................... 30 3.5 Biological Hazards............................................................................................... 32 3.6 Volcanic Hazards ................................................................................................ 33 3.7 Earthquake Hazard ............................................................................................. 35 3.8 Land Instability .................................................................................................. 36 3.9 Mine Subsidence: ............................................................................................... 39 3.10 Erosion Prone Land............................................................................................. 40 3.11 Wildfire Hazard .................................................................................................. 41 4.0 Managing Risks .............................................................................................43 4.1 Civil Defence and Emergency Management Act 2002 ............................................... 43 4.2 Building Act 2004 ............................................................................................... 43 4.3 Local Government Act 2002 ................................................................................. 44 4.4 Resource Management Act 1991........................................................................... 45 4.5 Northland Regional Council .................................................................................. 46 4.6 Whangarei District Council ................................................................................... 47 4.7 Iwi Management Plans ........................................................................................ 48 4.8 Community Response Plans.................................................................................. 48 5.0 Best Practice .................................................................................................49 5.1 Hard to Soft Mitigation Measures .......................................................................... 49 5.2 Recognising Vulnerable Populations ...................................................................... 49 5.3 Risk Management ............................................................................................... 50 5.4 Incorporation of Local Knowledge......................................................................... 51 6.0 Comparison of the Three Futures ..................................................................52 6.1 Future One: Lightly Regulated, Market Led Development (Business as Usual)............. 55 6.2 Future Two: Twin City/Urban and Coastal Spread .................................................. 59 6.3 Future Three: Satellite Town/Rural and Coastal Villages .......................................... 62 7.0 Conclusion.....................................................................................................66 8.0 Bibliography..................................................................................................68 Appendix 1: Key Provisions from NRC Regional Policy Statement ............................72 Appendix 2: Provisions from Whangarei District Plan (2007)...................................79 List of Figures Figure 1: Topographical Map of Whangarei ................................................................... 11 Figure 2: Broad Hazardscape Map for Whangarei ........................................................... 12 Figure 3: Total Rainfall (mm) Expected to Fall in a 24 Hour Period ................................... 14 Figure 4: Map of Flood Susceptible Areas...................................................................... 17 Figure 5: Map of Urban Flood Susceptible Areas in Whangarei District Plan ....................... 18 Figure 6: Average Annual PED. Comparison Between Average Years and El Nino Years. ...... 21 Figure 7: Coastal Hazard Lines Recorded in District Plan ................................................. 23 Figure 8: Storm Surge Example ................................................................................... 25 Figure 9: MHWS and Highest Astronomical Tide Above Mean Sea Level............................. 27 Figure 10: Maximum Water Surface Elevations For An Eastern Distant Source ..................... 29 Figure 11: Maximum Water Surface Elevations for the Tonga-Kermadec source ................... 30 Figure 12: Probability Maps of Potential Evapotranspiration Deficit..................................... 32 Figure 13: Location of Late Cenozoic Basalts and Associated Volcanics in Northland............. 34 Figure 14: Earthquake Scale with a Return period of 475 Years. ........................................ 36 Figure 15: Map of Stability Around the Whangarei Urban Area........................................... 38 Figure 16: Mining Hazard Maps from Whangarei District Plan: Hazard Areas........................ 40 Figure 17: Map of Erosion Prone Land ............................................................................ 42 Figure 18: Roles of Agencies in Civil Defence Planning ..................................................... 44 Figure 19: Broad Hazardscape Map overlaid with Future One ............................................ 57 Figure 20: Broad Hazardscape Map overlaid with Future Two ............................................ 61 Figure 21: Broad Hazardscape Map overlaid with Future Three .......................................... 64 List of Tables Table 1: Hazard Priority Listing................................................................................... 13 Table 2: Risk Categories for Qualitative Assessment ...................................................... 53 Table 3: Relative Percentage of Total Population in Geographical Area Type..................... 54 Table 4: Qualitative Analysis of Key Natural Hazard Exposure in Future One..................... 58 Table 5: Qualitative Analysis of Key Natural Hazard Exposure in Future Two .................... 62 Table 6: Qualitative Analysis of Key Natural Hazard Exposure in Future Three .................. 65 DRAFT VERSION 1 1.0 Introduction The purpose of this report is to provide an overview of the risks posed by natural hazards within the Whangarei District, and their implications for development. It includes a brief description of various natural hazards, summarises the legislative environment, and qualitatively assesses their influence or impact in terms of the three futures scenarios used in Sustainable Futures 30/50. The geographical features of Whangarei District such as the extensive coastline, variable geology and topography, and climatic variability mean that natural hazard events are a regular occurrence. This report is based upon presently available material from documents prepared by Northland Regional Council (NRC), the Institute for Geological and Nuclear Sciences (IGNS), the Ministry of Civil Defence and Emergency Management (MCDEM), and National Institute of Water and Atmospheric Research (NIWA) and others. It should be noted that this report excludes the most recent available material on climate change, and instead focuses on the present hazardscape1 of Whangarei District. However, some sections on flooding, landslides, and coastal hazards include some allowance for climate change, when this is explicitly provided for within the source material. This approach is not for the purposes of downplaying the significance of climate change and its potential impacts on Whangarei District. Instead it is felt that a separate report may be the most appropriate way of examining climate change impacts especially as they are not solely contained within the realm of natural hazards, but can affect economic output and other facets of community life. Taken as a whole, the following information and accompanying maps will be used to understand, and plan for, the constraints to development posed by natural hazards. It is recognised that much of Whangarei District, and the main settlements, are in areas of known risk and there will be some difficulties in alleviating that risk. But in terms of future development, it may be prudent to avoid some of the more serious natural hazards, which also reflects the trend in natural hazard management globally. 1.1 Natural Hazards: A Briefing The term “natural hazard” has been defined in various pieces of